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daved20319
06-13-2010, 10:01 AM
I'm into air rifles, nice ones, that's the primary reason I got a lathe. Recently, on one of my air gun forums, someone suggested creating an integral muzzle brake by boring out the muzzle end of the barrel larger than bore diameter. For the project rifle I'm working on, I like this idea. And if it turns out I don't like it in reality, I can always cut off the brake end and turn a brake I do like.

However, that brings up the question of how best to bore the end of the barrel. It was suggested that a piloted reamer would be the way to go, to maintain concentricity with the barrel bore. The concern is, wiping out the rifling with the pilot. Has anyone here tried something like this, and if so, how did you go about it? By all accounts, the steel used in air rifle barrels is quite a bit softer than firearms, so anything with a tool steel pilot will risk destroying the rifling. Is it possible to get a custom reamer made with a brass pilot, or is the pilot just not needed in this case? My intent is a 4-6" brake section, with an actual (rifled) barrel length of around 12", optimum for spring piston air rifles. Any suggestions or ideas would be much appreciated, thanks.

Dave

41mag
06-13-2010, 10:20 AM
you can buy counterbores with replaceable pilots held in with a set screw. maybe make your own pilot out of brass?

38_Cal
06-13-2010, 11:41 AM
41mag, you beat me to it! You can get removable pilot counterbores on EvilBay in the range of $15-$20. Look for aircraft counterbores, with a reduced diameter shank that you can solder to an extension...

David

deltaenterprizes
06-13-2010, 04:31 PM
On some piloted reamers for chambering rifle barrels the pilot is made to rotate so it does not wear the rifling in front of the chamber. The pilot spins on the screw that holds the pilot onto the reamer. You cold make one that does that.

quadrod
06-13-2010, 05:33 PM
Try contacting PTG. They can probably make any live piloted reamer you want.
http://www.pacifictoolandgauge.com/

huntinguy
06-14-2010, 02:28 AM
Hmmm. Interesting curiosity. If the material for the pilot is soft, I would think it could catch and gall the rifling. In short you would have a reverse reamer.

I would go with a hardened tool steel pilot. That way it could not gall and if it was polished very smooth (8 or better finish) I don't see how it could damage the rifling. I might even make the pilot extra long to engage as many lands as possible to spread out any pressure you might have.

But that is just me. :eek:

Rusty Marlin
06-14-2010, 03:01 PM
You are describing a live pilot and that's what you are going to want to use. Be very sure the nose of the pilot is stoned smooth and well rounded, if not it can dig into the rifling and gouge as its inserted.

How do you plan on deburing the the rifeling crown 4"-6" down inside the barrel? A pointed brass rod with lapping compound will work for this.


I've never done this on anything other than in high volume production on large caliber handguns but you might be able to make a drill rod guide that would be a slip fit in the barrel, install it from the chamber end. It would have a slip fit hole that fits the reduced shank of reamer with a live pilot. Remove the pilot from the reamer and use the guide tube as the pilot. We use this to eliminate the posability of the live pilot picking up a chip between the pilot and the reamer, getting stuck and start spinning on the rifing.

motorcyclemac
06-18-2010, 02:09 AM
I second QuadRod's suggestion

Contact Pacific tool and Gauge in Oregon.

Ask to talk to Dave Kiff. He is my contact there and is a true professional in his line of work. He will make you what ever tooling you could ever need. Something simple like you need would probably run you $100 +/_.

They make nothing but top shelf tooling in my opinion. Very high quality and long lasting.

Cheers
Mac.

Forestgnome
06-20-2010, 11:17 AM
I don't get it. What's the point of a muzzle brake on an airgun? Best way would be to chuck the barrel in a lathe and go to it.

Jim Shaper
06-21-2010, 03:35 AM
I don't understand why you want such a long section of unsupported flight inside the barrel?

A brake is intended to divert the gasses away from the projectile so that any movement of the gun after the bullet has cleared the muzzle won't throw the tail off and effect the bullets stability and thus trajectory.

With a spring air gun, the only effect the modification you propose has is in reducing the report. Having a chamber even half an inch deep will likely result in the effect you're after, and you can easily do this with a boring bar.

daved20319
06-22-2010, 12:24 AM
And here are some answers for the last couple of responses.

Forestgnome, a muzzle brake on an airgun is primarily for looks, although with break barrel guns, they can also act as cocking aids by increasing barrel length, thus leverage.

Jim Shaper, optimum barrel length in a spring piston air gun is somewhere around 12". Problem is, a 12" barrel doesn't give much leverage when cocking a break barrel air gun, and that can take all the joy out of shooting in a real hurry, especially if you're shooting a "magnum" air gun. Adding a brake to increase the leverage is common practice. But when the idea of an integral brake was suggested, the idea of the unbroken barrel line really appealed to me, which is what resulted in my original post.

As to reducing the report, it's unlikely. A brake may change the tone, but springers are pretty quiet to start with, and most of the noise comes from the power plant. Air rifles are usually sub-sonic, it's the nature of the ammo we shoot. In fact, accuracy suffers the closer you get to the speed of sound, and totally goes to hell when you exceed it. So although you can push some over 1100 feet per second, optimal speed with most pellets is between 800 and 900 feet per second. There are some exceptions, but they're not the norm, and they also tend to be VERY expensive! Of course, air gunners are crazy, a modestly priced quality air rifle is in the $300 range, high end guns can exceed a grand, and some go for MUCH more. Like I said, crazy :-)! Later.

Dave

Jim Shaper
06-22-2010, 01:06 AM
I've got a buddy who's done chrono'd chopped barrel testing and he says muzzel velocity wasn't reduced at 4", but that cocking was a nightmare. When you can get the gun for 100 bucks, it makes for a playground to some folks. I spend that much in ammo every time I hit the range.


Out of curiosity, why don't you port the barrel?

daved20319
06-22-2010, 11:19 AM
I don't know, Jim, porting has been tried with air rifles, but it has little if any effect on springers. The spring piston design produces high instantaneous pressures but with a very low total volume of air, and when everything is properly balanced, you really have little if any extra gasses to be ported.

The pre-charged pneumatic (PCP) power plant, on the other hand, uses lower pressures, "only" 3000 psi, but much greater air volume. Ports, brakes, air strippers, and even silencers are used on PCP's to good effect. Because of the much greater air volume, longer barrels make sense. In fact, up to a point, the longer the barrel, the greater the power, 20-24" is common, and some have been made with barrels up around 30".

My apologies if this is turning into too much info, but I AM one of those crazy air gunners :-). Powder burners are great, and I have a couple of nice ones, but the air guns get shot FAR more. At a penny or two a shot vs. $1 or more for my .308, and being able to step out my back door and shoot to my hearts content, they really can get addictive. Later.

Dave

Jim Shaper
06-22-2010, 12:11 PM
I'm confused by what you're supposedly gaining with counter boring your spring air barrel.

daved20319
06-22-2010, 05:59 PM
The idea is to have a rifle section approx. 12" long, with the counter bored "brake" section approx. 4" long, for a total barrel length of approx. 16". This will give me enough barrel length for good leverage so that cocking isn't a major upper body workout, while still giving me that optimal 12" barrel length. It will also get the rifles overall length down below 40", a length that works nicely for me. And all without an add on brake or shroud that can work itself loose, usually at the worst possible time. Sorry for the confusion, hope that clears it up. Later.

Dave

Jim Shaper
06-23-2010, 04:56 AM
Yet you don't think all that air wooshing around your pellet is going to cause you problems?

Forestgnome
06-24-2010, 09:49 AM
The idea is to have a rifle section approx. 12" long, with the counter bored "brake" section approx. 4" long, for a total barrel length of approx. 16". This will give me enough barrel length for good leverage so that cocking isn't a major upper body workout, while still giving me that optimal 12" barrel length. It will also get the rifles overall length down below 40", a length that works nicely for me. And all without an add on brake or shroud that can work itself loose, usually at the worst possible time. Sorry for the confusion, hope that clears it up. Later.

Dave
Why not just leave the barrel 16" long? Are you saying a 12" barrel is more effective than a 16" barrel?

oldstarfire
06-24-2010, 10:14 PM
I installed a 4 inch long "brake" on a 177 spring type, inside hole was about 1/2 inch diameter - more for weight and leverage than anything.
Accuracy was non-existent.
Removed it and was back to normal.
I have suspected that the air blast was the problem.

daved20319
06-25-2010, 10:00 AM
Jim, it's been done on lots of air guns, sometimes it works, sometimes it doesn't. It is pretty common practice, especially on the guns sold at Wally World. That supposed "cool factor", don't ya know :-)? Again, it's a balancing act. Get it right, and there really isn't much air to upset the pellet. But barrel length isn't the only part of the equation, there's piston and top hat (please don't ask) weight, spring, guide, piston seal, and pellet selection, in no particular order. Change one thing, and everything else changes, of course.

Forrestgnome, at least in theory, a 12" barrel is more EFFICIENT than a 16" barrel, and for at least a couple of reasons. One, at 12", you're getting all the velocity you can from the available air, and not losing any to barrel friction. And two, you're getting the pellet out of the barrel quicker, thus decreasing the time the loose nut behind the trigger has to screw up the shot :-). I'm sure there are others, but those are the most frequently mentioned. As always, there's a caveat here. You still need to keep velocity sub sonic, most pellets aren't stable past about 900 fps.

Oldstarfire, I've heard the same before, although it's fairly rare, and usually has to do with alignment and pellet clipping. Most air guns seem to do fine with brakes, even fairly long ones. Part of it is that balancing act I mentioned above. Based on my own experience, I think a 1/2" hole was too big, most .177 brakes are typically about 1/4". I've never had an accuracy issue with an airgun that I could attribute to a brake or lack thereof. Lots of things can play into it, but most accuracy problems with springers are caused by the shooter trying to shoot one like a center fire rifle. I don't want to go into a treatise on shooting springers here, but it takes a specific and consistent technique to shoot them well. Powder burners are far more forgiving in this regard.

I want to thank all of you for responding to this post. Actually writing it down has made me realize a couple of things, first, I've learned a hell of a lot about air guns in just a few years, and second, I've got a hell of a lot to learn :-)! Later.

Dave